A typical automotive air conditioning system includes a compressor, a condenser, an expansion device, and an evaporator. Hydraulically connecting the aforementioned components are series of refrigerant tubes that are capable of conveying a two phase refrigerant operating under high and low pressure flows. An exemplary two phase refrigerant commonly used in a typical modern automotive air conditioning system is an environmentally friendly refrigerant known as R-134a and low Global Warming Potential (GWP) refrigerants such as HFO-1234yf.
The compressor is commonly referred to as the heart of the air conditioning system in which it is responsible for compressing and transferring the refrigerant throughout the system. The compressor includes a suction side having a suction reed valve assembly and a discharge side having a discharge reed valve assembly. The main inner volume of the compressor, the so called crankcase, is substantially hollow, but numerous moving components are either contained in or exposed to the refrigerant, such as the central drive shaft, shaft support bearings, swash plate, and reciprocating variable displacement pistons.
The evaporator is disposed in the passenger cabin of the automobile and the condenser is disposed in the front portion of the engine compartment or more precisely, in front of the radiator exposed to the outside ambient air. Heat energy from the passenger cabin is absorbed by the refrigerant in the evaporator and conveyed to the condenser where it is dispelled to the ambient air. Within the evaporator, a low pressure liquid refrigerant (LPLR) expands into a low pressure vapor refrigerant (LPVR) by absorbing heat energy from the passenger cabin. The LPVR exiting from the evaporator is drawn by the compressor and compressed into a high pressure vapor refrigerant (HPVR). The compressed HPVR is then discharged by the compressor to the condenser. As the HPVR passes through the condenser, the refrigerant is condensed into a high pressure liquid refrigerant (HPLR) as it releases the heat it absorbed from the passenger cabin to the ambient air outside of the automobile. Exiting the condenser, the HPLR passes through an expansion device that regulates the flow of the now LPLR to the evaporator to repeat the process of heat transfer from the cabin to the outside ambient air.
The temperature of the returning LPVR to the compressor from the evaporator is typically 40° F. to 100° F. lower than the HPLR exiting the condenser. An internal heat exchanger, such as the internal heat exchange having an internal spiraled or helical tube disclosed in U.S. patent application Ser. No. 12/487,709 is used to take advantage of the temperature differential between the lower temperature LPVR and the higher temperature HPLR to improve the overall cooling capacity of the air conditioning system. The internal heat exchanger includes an outer pipe and a co-axially located helical coiled tube located within the outer pipe. The relatively cooler LPVR exiting the evaporator is passed through the outer pipe and the relatively hotter HPLR exiting the condenser is passed through the helical coiled tube. Heat is transferred from the HPLR exiting the condenser to the cooler LPVR returning to the compressor in the internal heat exchanger. By decreasing the temperature of the HPLR prior to it flowing through the expansion device, the expansion device may be set at a lower temperature; therefore the temperature of the LPLR entering the evaporator is at a lower temperature to increase cooling efficiency of the air conditioning system.
During periods of low demand on an automotive air conditioning system, the mass flow rate of the LPVR entering the suction side of the compressor would occasionally drop below a certain threshold which would cause what is commonly referred to as compressor pulsation rattle. The compressor experiences pulsation rattle due to the suction reed becoming unstable by fluctuating between a partially opened and closed position. The fluctuating suction reed sends an acoustic wave upstream through the system's refrigerant tubes and internal heat exchanger toward the evaporator. The evaporator amplifies the acoustic wave resulting in undesirable noise and vibration that may be noticeable to occupants within the passenger cabin. The compressor pulsation rattle can be reduced or eliminated by increasing the mass flow rate of refrigerant to the suction side.
To compensate for the occasional low mass flow rate of the vapor refrigerant to the suction side of the compressor, it is desirable for an air conditioning system to have a bypass device to augment the occasional low mass flow rate of the low pressure suction side with refrigerant from the high pressure discharge side of the compressor. It is further desirable to have such an air conditioning system that can augment the low mass flow rate of the low pressure side of the compressor on a self regulating, as needed basis. It is still even further desirable to have an existing component of the air conditioning system, such as the internal heat exchanger, that can accomplish the above mentioned functions.